Obsessional disorder of childhood is a rare disorder about which little is known. In this protocol we have collected basic data on family history of mental illness, sleep measures, CAT Scans and neuropsychological testing on seventeen children and adolescents with obsessional disorder, and age/sex/handedness matched controls. Major findings to date are a higher Ventricular Brain Ratio (VBR), and decreased visuo-spatial ability in patients compared with controls. Clinically, these children did have mild pre-morbid temperment, but had few obsessive-compulsive traits before developing the disorder; state and trait appear discontinuous. A drug trial of chlorimipramine or placebo has been carried out to evaluate the effect of the antidepressant and the specificity of chlorimipramine for this disorder.